Compressor



Jan;- 10,v 1939. R BAKER 2,143,179

COMPRESSOR Filed Aug; 20, 1937 g Iinventor 5 4o 4 BB 4'1 I law.

attorneys both steam cylinders being tripped by the high stroke.

Patented Jan. 10, 1939 UNITED STATES PATENTOFFICE 2.143.119

E.Bakcr,lceading,Mass.,assignortoThe New Iork Air Brake Company, a corporation of New Jersey Application August 20, 1937, Serial No. 160,156

. 2,0laims.

This invention relates to air compressors and particularly to cross compound steam driven two stage compressors oi the type extensively used on steam locomotives to charge the main reservoir of the air brake system.

The principal object of the invention is to facilitate starting of the compressor, and particularly to prevent stalling of the compressor,

when the governor acts to start it after'a shut down.

In such compressors the steam end is doubleacting and cross compound, the valve gear for pressure piston as it approaches its two limits of V The air and is two stage and comprises two double acting cylinders withflrst stage inlet valve, interstage valves, and high pressure discharge valves, all of the automatic (poppet) type and all set to close by gravity. The high pressure steam piston drives the large, first stage (low pressure) air piston, and moves reversely with respect to the low pressure steam piston which drives the second stage (high pressure) air piston.

The pistons oi the two stages are not mecharr.

ically connected, but their motion is timed by the steam valve gear. 7

Such compressors have long been in extensive use. Their outstanding merit has been the utter reliability, so necessary in railway brake service. Recently improved workmanship, such as lapped cylinders and special tight sealing piston rings, have markedly improved performance. Unfor; tunately introduction of these improvements was soon followed by numerous complaints as to compressors stalling. Examination of such stalling compressors showed them to be in perfect working order. Since suchstalling is often seriously. dangerous and at best causes intolerable traflic delays, immediate solution of the difliculty was necessary. 3 a The present invention is based on applicants discovery of the cause of such stalling.

If, when the compressor is stopped, a high pressure air discharge valve fails to seat tightly for any reason, and they occasionally do so, the main reservoir air (at say 140 pounds gage) feeds back to the high pressure cylinder and loads the intermediate valves so that they cannot open until pressure in the low pressure cylinder attains an equal value. I! the compressor has stoppednear the commencement of the compression stroke in air cylinder will balance the boiler pressure com monly used in the high pressure steam cylinder. Hence the high pressure steam piston cannot move far enough to trip the valve gear, with the result that the compressor stalls.

with the somewhat leaky air pistons formerly used, air escaped around the piston and the compressor started after slight delay. with modern tight pistons a stalled compressor would not start at all. The usual, but very objectionable expedient, was to bleed the main reservoir, whereupon the compressor would start and would continue to operate satisfactorily for an unpredictable period, i. (2., until a discharge valve failed to seat tightly as the pump stopped.

According to the present invention automatic relief valves-of limited flow capacity are put in both working spaces of the low pressure air cylinder. With a normal low pressure discharge pressure of the order of 40 pounds gage and a stall-- in pressure of the order of 76 pounds gage, the

preferably are made of small flow capacity, to the end that failure of a relief valve will not disable the pump completely. This detail is a feature of the invention. I

In connection with the restricted flow princiing andensure quiet operation.

Other features of invention reside in specific details of construction, such as mounting the relief valve in the inlet valve cap for one end of the cylinder, and in an intermediate valve cage for w the other end of the cylinder, such arrangements ofiering simple modes of applying the relief one of the low pressure air work n spaces, the 1 valves, without change in the design of existing compressors.

The invention will now be described in detail in connection with the accompanyin drawing, in which:

Fig. 1 is a diagrammatic section of a cross compound two stage airoompressor showing the invention' applied; r

Fig. 2 is an axial section through an intermediate valve cage with relief valve applied.

Fig. 3 is an axial 'sectionof a low pressure valve cap with the invention applied.

inlet pie, special construction is used to prevent squeal- Referring first to Fig. 1, 3 represents the high. pressure steam cylinder; and I the low pressure steam cylinder of a cross-compound unit for driving a compressor. 31s the double-acting high pressure steam piston and 9 is the double-acting low pressure steam piston. The high pressure piston 8 is connected by rod II with the low pressure or first stage air piston l2 which works in the low pressure air cylinder l3. The low pressure steam piston 9 is connected by the rod. l4 with the high pressure (second stage) air piston l5 which works in the high pressure air. cylinder l6. I1 is the steam supply connection which" leads to the main steam distributing valve l8. This valve is shifted between its two limiting positions by steam pressure under the control of a pilot valve IS, The pilot valve I9 is shifted between its two limiting positions by a rod 2i having a shoulder 20, and terminating at its lower end in a button 22. A plate 23 attached to the high pressure steam piston 8 embraces rod 2|, and coacts with button 22 and shoulder to shift rod 2i near the opposite ends of the piston stroke.

The steam valve mechanism is shown'in position to cause the downward excursion of the high pressure steam piston 8 and the simultaneous upward excursion of the low pressure steam piston 3. The high pressure piston 8 is shown in the position in which the plate 23 is just about to pick up the button 22 and shift the pilot valve I9 downward. Downward-shifting of the pilot valve i 3 causes the shifting of the main distributing valve id to its 'extreme right hand position. Such reversal causes the upward excursion of the high pressure ,nothing novel in the steam end of the pump illustrated. For this reason, and for the further reason that pumps of this type are very well known in the art, it seems unnecessary to describe in detail the porting of the steam end, beyond pointing2 out that the exhaust passage is indicated at 5.

In pumps of this type the steam valve mecha nism is in 'a steam head 26 common to the two steam cylinders 6 and I. A so-called center plate 21 serves as spacing means between and as heads for the lower ends of the steam cylinders 6 and I, and upper ends of'the air cylinders l3 and It. This center plate carries packing glands 28 for the piston rods H and I 4, and also the low pres sure inlet valve, and the intermediate valves (two, arranged in parallel) for the upper working space 'of theair compressor. A lower head 29 closes the lower ends of the 'air cylinders andcarries the inlet valve and the intermediate valves (two, ar ranged in parallel) for the lower working space of the'air compressor.

Since all air valves are of the automatic poppet typ and are arranged to seat by gravity, the

.porting for the valves of the up'perand lower working spaces of the compressor differs in form (though not in function). This entails structural diiferences in the application of the relief valves for the twoends of the low pressure air cylinder. l Generally stated, for the upper working space, the low. pressure inlet valve and the intermediate valves aremounted under removable screw caps,

and the cap over the: inlet valve is readily availed of to carry the relief valve. For the lower working spacethe corresponding valves are mounted in' removable cages. In consequence, the relief valve cannot conveniently bemounted in the inlet shown at 63. The discharge valves are-shown valve cage, but can very simply be mounted on the cage of one of the intermediate valves. The reason for the difference of location having been explained, the structure can be described.

Referring first to the upper working space, Si is the air inlet passage leading to seat 32 of inlet valve 33, from which passage 34 leads to the upper working space above piston l2. Removable cap 35 is. modified according to the invention. It is counterbored from the top and threaded at 36 to receive relief valve housing 31, having a restricted outlet port 38 (see Fig. 3). Through ports 4|! are formed in the cap. Screwed into the lower end of housing 31 is member 39 having a center port 4i substantially larger than port 38 and a suragainst reverse fiow. They follow standard construction.

Referring now to the lower working space, the inlet air passage 5i leads through ports in cage 52 (threaded into head 29) to the seat 53 of inlet valve 54. This valve controls inlet to the lower working space in cylinder i3, and follows standard construction. One of the two intermediate valves is unchanged, but the cage of the other is modified to carry a" relief valve. coacts with a seat in a ported cage 56 which is screwed into head 29 as usual. The other valve 51 coacts with a seat 58 in a modified cage 53, shown in detail in Fig. 2. Valves 55 and '5] permit parallel flows from space 6|, in, communication with the lower working space of cylinder l3, to passage 62 which leads to the lower working space in cylinder l6.

Referring now to Fig. 2, the modified cage 59 is counterbored and threaded at its outer end to receive a relief valve housing 31a, identical with housing 31. Through ports 60 are formed in cage 59 to lead to the relief valve. The parts 31a to 39a and Mo to 45: correspond to similarly numbered parts in Fig. 3, in fact, these parts comprise identical and interchangeable relief valves. Each permits flow from a corresponding low pressure working space to atmosphere.

In each relief valve the spring 44 (44a) offers such resistance that valve 43 (43a) will not open until the normal intermediate pressure is definitely exceeded, but will open at a pressure below that which would stall the high pressure steam piston under the minimum boiler pressure encountered in service. outflow to a rate so low that even if the corresponding' valve 43 (43a) should fail to seat the pump will still operate with substantial capacity. By-making port 38 smaller than port 4l the tendency of the relief valves to squeal is virtually eliminated. 1 I

The discharge connection of the compressor is at 64 and 65 and are of familiar form.

The structure, above described in considerable detail, is intended to beillustrative and not limiting.

The invention has given complete success in service, is easily applied to new or old compressors at small expense, does not impair the efficiency of the compressor, and does not introduce acomponent whose failiire\would disable the compressor.

In Fig. l the valve 55.

Port 38 (38a) restricts the What is claimed is: w 1. The combination of a double acting stage -gas compressor including high and low pressure steam motor pistons respectively connected to first and second stage compressor pistons, and compound steam distributing valve gear arranged to be reversely shifted by the high pressure steam piston near the limits of its working strokes; and loaded relief valves for relieving pressure in the working spaces of the compressor first stage, said valves being arranged to open at a pressure higher than the maximum reached in said spaces during normal operation, and lower than that pressure which will stall the high pressure steam piston under the lowest available high pressure steampressure.

2. The combination of .a double acting stage gas compressor including high and low pressure stem 3 motor pistons respectively connected to first and second stage compressor pistons. and compound steam distributing valve gear arranged to be reversely shifted by the high pressure steam piston near the limits of its working strokes; loaded relief valves for relieving pressure in the working spaces of the compressor first stage, said valves being arranged to open at a pressure higher than the maximum reached in said spaces during normal operation, and lower than that pressure which will stall the high pressure steam piston under thelowest available high pressure steam pressure; and means for throttling flowthrough said relief valves to a rate which will not seriously impair the operation of thecompressor should a relief valve 15 fail to close.

ROY E. BAKER. 

